Two months after the election, Florida law enforcement authorities are closing several voter fraud investigations after finding no evidence of wrongdoing.

One of the biggest cases closed so far: Allegations of voter fraud surrounding 20 people who registered to vote through the website of Rock the Vote. The nonpartisan group partners with MTV and relies on popular musicians to help encourage people to register.

Florida Department of Law Enforcement agents interviewed people across the state and concluded that no criminal activity took place.

"We take our jobs of registering voters very seriously, and evaluate and test our programs and technology on an ongoing basis, so we were not surprised that the investigation found that we did nothing wrong," said Chrissy Faessen with Rock the Vote.

The investigation was trigged by the Florida Department of State, which questioned the validity of some registrations. On Thursday, the agency refused to release the information that it used to spark the investigation.

While the Rock the Vote case is closed, several major cases remain open.

They include an investigation involving a company hired by the Republican Party of Florida to register voters. Strategic Allied Consulting was paid at least $1.3 million for the work and also was hired by Republicans in other battleground states. Florida Republicans fired the company after learning of the problems.

Authorities also are looking into fake letters that carried a Seattle postmark and questioned the citizenship of voters, many of them Republicans. That investigation is being led by the FBI, according to correspondence sent to county election officials last October.

Voter fraud complaints registered against several other organizations, including the Florida Democratic Party, remain under investigation, an FDLE spokeswoman said Thursday.

Another recent case that has been closed involved whether one voter had cast ballots in both Florida and Rhode Island. The case was initiated by the group called True the Vote, which initially said 36 people had voted in Florida and other states.

FDLE closed the case after state election officials were told by Rhode Island authorities that the name of the voter there was probably wrong and was listed incorrectly because of a poll worker's error.